US 7442938 B2
A detector includes a reflector and a scintillator in optical communication with the reflector, wherein both the reflector and the scintillator are fabricated from the same material.
1. A detector comprising:
a reflector; and
a scintillator in optical communication with said reflector, both said reflector and said scintillator are fabricated from the same material wherein said material is milled to a sub micron size, and comprises at least one of Y—Gd—Eu—O:Pr, Gd—S—O—Ce—Tb, and Lu—Tb—Al—O:Ce.
2. A detector in accordance with
3. A detector in accordance with
4. A method comprising:
creating a compound comprising at least one of Y—Gd—Eu—O:Pr, Gd—S—O—Ce—Tb, and Lu—Tb—Al—O:Ce, wherein said compound is milled to a sub micron size;
using the compound both as a scintillator and as a reflector; and
applying an optical reflector film to a top reflector surface.
5. A method in accordance with
6. A method in accordance with
7. A method in accordance with
8. A CT system comprising:
an x-ray source configured to emit x-rays;
an x-ray detector positioned to receive x-rays emitted by said source; and
a computer operationally coupled to said source and detector, said detector comprising a reflector and a scintillator in optical communication with said reflector, both said reflector and said scintillator are fabricated from the same material wherein said material is milled to a sub micron size, and comprising at least one of Y1.33Gd0.66Eu0.01O3:Pr, Gd2(S,O)2:Ce,Tb, and Lu0.8Tb2.2Al5O12:Ce.
9. A system in accordance with
This invention relates generally to imaging methods and apparatus, and more particularly, to methods that provide for improvements in x-ray detector fabrication and resulting apparatus.
X-ray detectors typically include a photodiode portion and a scintillator portion. An x-ray enters the detector and impinges the scintillator material, wherein photons of visible light are created. The visible light then leaves the scintillator material and impinges a photodiode. The photodiodes are polled, returning attenuation measurements. This data is then used to create images. Each scintillator pixel has a corresponding photodiode, and it is desirable that all light generated in the scintillator be directed toward the photodiode, therefore reflective material is used to reflect light directed in directions other than the photodiode direction. In other words, one can imagine a scintillator cell as a six sided cube, with one side facing the photodiode and the five other sides having reflective material. The side opposite the photodiode is termed the top side.
One known scintillator array (commonly called a “cast pack”) used in Computed Tomography (CT) uses a cast reflector coating as its light reflector. The reflector is epoxy filled with a highly reflective powder such as TiO2. The cast reflector coating typically mechanically bounds the scintillator pixels together to form an array and the cast reflector coating also reflects the light back into the pixels from the surface. This reflector is important for light collection efficiency purposes. One problem in the known reflector process is the curing shrinkage of the epoxy and the thermal expansion mismatch between the reflector and the ceramic scintillator pixels. The reflector has about 70% to 80% epoxy in volume. After curing, the epoxy will shrink by more than 5% in volume. While it shrinks, the adhesion is already being developed between the ceramic and reflector. This shrinkage causes very high stress on the interface and also inside the ceramic pixels. This stress can lead to cracks of the ceramic pixels, and delamination between the reflector and ceramic pixels. A wire saw is typically used to perform geometric dicing and pixelating of the packs before the casting, and this shrinkage problem becomes more damaging. The curing stress can cause the packs to bow along both the X and the Z directions. This in turn can cause the pixels to tilt and can cause pixel misalignment. The bowing can also cause other process related problems because of the lack of the flatness of the packs.
Therefore, below are described methods and apparatus that at least partially solve the above described problems.
In one aspect, a detector includes a reflector and a scintillator in optical communication with the reflector, wherein both the reflector and the scintillator are fabricated from the same material.
In another aspect, a method includes creating a compound, and using the compound both as a scintillator and as a reflector.
In yet another aspect, a CT system includes an x-ray source configured to emit x-rays, an x-ray detector positioned to receive x-rays emitted by the source, and a computer operationally coupled to the source and detector, the detector including a reflector and a scintillator in optical communication with the reflector, wherein both the reflector and the scintillator are fabricated from the same material.
There are herein described methods and apparatus useful for imaging systems such as, for example, but not limited to an x-ray system. The apparatus and methods are illustrated with reference to the figures wherein similar numbers indicate the same elements in all figures. Such figures are intended to be illustrative rather than limiting and are included herewith to facilitate explanation of an exemplary embodiment of the apparatus and methods of the invention. Although, described in the setting of an x-ray system, it is contemplated that the benefits of the invention accrue to all diagnostic imaging systems, all current modalities and/or any modality yet to be developed in which scintillators and reflectors are used.
Herein described is a reflector fabricated from a porous ceramic material that has the same composition as the scintillator. The ceramic reflector has no cure-related shrinkage and very small if any thermal expansion mismatch with the ceramic scintillator pixels, so using a ceramic reflector can solve all the cure shrinkage related problems experienced by the known pack manufacturing process. The use of a ceramic reflector can also reduce the x-ray punch-through and some of the x-ray caused crosstalk between the pixels.
It is contemplated that the benefits of the invention accrue to human and non-human imaging systems such as those systems typically employed in small animal research. Also, it is contemplated that the benefits of the invention accrue to non-medical imaging systems such as those systems typically employed in an industrial setting or a transportation setting, such as, for example, but not limited to, a baggage scanning CT system for an airport or other transportation center as shown in
Referring now to
The above calcined powder can also be used to make the reflector material for the above pixilated packs resulting from the steps in
A pixilated scintillator pack 232 made at least partially in accordance with the steps listed in
The herein described methods and apparatus will allow for relatively minimal curing related shrinkage. Thus, there is little or none pack bowing and/or delamination. Although one embodiment uses 64 slices, the ideas herein expressed are expendable to longer packs beyond 64 slices. The methods and apparatus herein described allow for less stress due to better thermal expansion matching of the reflector and the scintillator ceramics. Also empirical results have shown in the herein provided methods and apparatus allow for lower radiation damage than known epoxy based reflector methods and apparatus.
Also provided herein is lower x-ray caused crosstalk due to the higher density of reflector. There is also an higher light output due to the extra light generated by the scintillator powder in the reflector.
As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.
Technical effects include that the herein described methods and apparatus allow for a CT scintillator array (pack) using the same composition ceramic as a reflector.
Exemplary embodiments are described above in detail. The assemblies and methods are not limited to the specific embodiments described herein, but rather, components of each assembly and/or method may be utilized independently and separately from other components described herein.
While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.